Is very easy add and substract graphically. One can regroup the tokens of each order, regroup, carry or borrow tokens, and you can obtain the result.
But not so easy to practice multiplication or division in this visual and interactive way.
I tried to think as a research physicist of the atom:
I looked the inside of the numbers:
Inside the numbers there are the components of the number: The prime factors.
To multiplicate two integers you must regroup the components of the two numbers.
To divide a integer, you must separate the components.
The program only works with integers. adds, subtract, multiplies and divides (but only exact division) using the prime factors of the numbers.
The behavior of places and tokens of this app describes the behavior of the numbers in the ℤ set.
Videos:
Touch Integers ℤ (+ - × ÷)

Touch Natural Numbers:
Small laboratory of Natural Numbers:
The Prime numbers are like the building blocks of the numbers.
With this app you can:
Analyze the factors of a Composite number.
Build a Composite number from its factors. (multiplication and division of Natural Numbers)
Localize or select a number in the Ulam Spiral.
Verify all the possible products between Primes in a composite number with the Parabolic Sieve.
Analyze or build a number with the Place Value activity (Addition or Subtraction)
Understand the Modulo of a number.
Introducing the polygonal numbers.
Know the numbers as the sum of two prime numbers or as the sum of three prime numbers.Touch Natural Numbers (video)

Base 10 blocks manipulative: Integers are transformed into small blocks. That can be manipulated to solve elementary operations. Is useful to teach about numbers, place value, and elementary operations.
Matters: borrowing in subtraction, adding positive and negative numbers, multiplication by negative numbers....

Camera Patchwork:
The application allows 360 degree views.
The program builds the image using a projection of the sphere similar to Mollweide.
The images are constructed from 300 small images.
The camera takes a picture when it detects a new spin 8 degrees in either direction.
Move the camera slowly.
We recommend vertical sweeps, moving to the right or the left.
Free appCamera Patchwork Gallery: